1. Field of the Invention
This invention relates generally to photographic apparatus and particularly to an interlock mechanism for use as an adjunct with a manually operated processing system to prevent the processing of non-exposed film units.
2. Description of the Prior Art
Manually operable photographic systems for consecutively exposing and processing a plurality of film units generally include interlock mechanisms that safeguard against the occurrence of anomalous user operations which result in picture losses. In cases where film units are of the self-processable type, it is a typical system requirement that processing occur following exposure and before a subsequent exposure can be made. With such film it is, therefore, a necessity to provide a processing system with intrinsic constraints that forces the user to act in a manner consistent with the logic of the system. The present invention when used as an adjunct with the processing system described in the above cross-referenced U.S. application Ser. No. 535,377 provides such a safeguard. The processing system in that application is intended for use with a type of film cassette that basically comprises a box-like plastic housing containing a stack of self-processable film units as, for example, described in U.S. Pat. No. 3,415,644 issued to Edwin H. Land on Dec. 10, 1968, and entitled NOVEL PHOTOGRAPHIC PRODUCTS AND PROCESSES. In these type cassettes each film unit is adapted to be consecutively exposed and subsequently withdrawn through an exit slot in the cassette and, afterwards, processed by being transported between a pressure generating nip defined by a pair of juxtaposed rollers located exterior to the cassette in close proximity to the exit slot.
The functions that a processing system must perform in order to satisfy the requirements imposed by such a film cassette are to: (1) selectively engage an individual exposed film unit within the cassette; (2) advance the engaged film unit from the cassette through its exit slot and into contact with the rollers; (3) rotate the rollers so that they further advance the film unit and process it as it is being moved by and through them; and (4) reinitiate the cycle to repeat the process in subsequent film units. Additionally, an energy source must be provided to supply the power required to drive the system.
In known manually driven processing systems for use with cassettes such as that described in U.S. application Ser. No. 485,795 entitled PHOTOGRAPHIC FILM CASSETTE, filed on July 5, 1974, by Nicholas Gold, the mode of operation after exposure may be described as follows: (1) the rollers are caused to rotate by some suitable manual power input such as a crank or lanyard; (2) a film advance is initially driveably connected to the power input such that it moves an exposed film unit out of the cassette and into engagement with the rotating rollers; (3) a clutch or cam mechanism interrupts the driving relationship between the film advance and the power input after the film unit is operatively associated with the rollers; (4) the power input continues to rotate the rollers and completes the processing of the film unit; and (5) a hold-release mechanism temporarily prevents the film advance from moving a subsequent film unit for processing until the previously exposed film unit has been processed and the release feature activated. Systems in the prior art exhibiting these characteristics are, for example, U.S. Pat. No. 3,757,657 entitled MANUALLY OPERABLE FILM-ADVANCING APPARATUS issued to Vaito K. Eloranta and Benjamin C. Ruggles on Sept. 11, 1973, and U.S. Pat. No. 3,810,210 entitled FILM UNIT PROCESSING MECHANISM issued to Henry S. Adamski and Guilford E. Kindig on May 7, 1974. The former includes a crank power input and the latter a lanyard power input.
Both of the aforementioned systems may be characterized as being relatively complex expensive mechanism since they employ the use of multiple gears and either a clutch or cam arrangement to terminate the power drive relationship between the rotating rollers and the film advance.
The present invention provides the temporary hold-release mechanism function of the prior art in a manner that is different from the prior art but consistent with the operating principle of a processing system described, for, example, in the aforementioned related U.S. application Ser. No. 535,377. As a consequence of the combination of the instant invention with a processing system such as that referred to, it is felt for reasons that will become apparent, that a relatively simple inexpensive interlock mechanism has been provided.